1. Technical Field
The present invention relates to a piezoelectric motor, a drive circuit, and a drive method.
2. Related Art
A piezoelectric motor is for rotationally driving a rotating body using a piezoelectric actuator provided with a piezoelectric element. The piezoelectric actuator used for the piezoelectric motor is provided with a vibrating member and the piezoelectric element for vibrating the vibrating member. In such a piezoelectric actuator, by applying a voltage to electrodes of the piezoelectric element to thereby longitudinally vibrating and flexurally vibrating the vibrating member, a protruding section provided to an end of the vibrating member is made to perform an elliptic motion. Since the protruding section elliptically moving has contact with a side surface of the rotating body, the rotating body rotates (see JP-A-2010-233339).
In order to make the vibrating member longitudinally vibrate and flexurally vibrate, a sinusoidal voltage is applied to the piezoelectric element to thereby resonate the vibrating member. In contrast, since the piezoelectric motor drives the rotating body while making the protruding section have contact with the side surface of the rotating body, a back electromotive force is caused in the piezoelectric element due to the reactive force by the contact. The inventors of the invention have found out a phenomenon specific to the piezoelectric motor that the current flowing through the piezoelectric element is distorted as a result.
In addition, in the circuit in which the amplitude of the current is reduced when the motional impedance is high, if the rotating body becomes difficult to rotate (i.e., the motional impedance is high), the rotating body becomes more difficult to rotate. Therefore, there is also a problem that the movement of the piezoelectric motor becomes unstable.